Faulty DNA repair appears to be the cause of Huntington disease, according to a new study led by researchers at the Mayo Clinic in Rochester, Minn (Kovtun IV et al. Nature. doi:10.1038/nature05778 [published online ahead of print April 22, 2007]).

An accumulation (over time and with each successive generation in an affected family) of extra CAG nucleotides within the gene that encodes the protein huntingtin creates an abnormal version of the protein that has a destructive effect in the brain. The scientists found that this CAG expansion occurs when cells attempt to remove oxidative lesions within the DNA through a repair enzyme called 7,8-dihydro-8-oxoguanine-DNA glycosylase (OGG1).